Do Mercury Warnings Apply to Both Farm Raised and Wild Trout?

January 15, 2009

Question: When DFG releases trout from one of your hatcheries, can these trout be considered farm raised or are they treated much differently than farm raised (e.g. fed antibiotics, growth hormones or other “unnatural” stuff)? Do the same mercury warnings apply to them as is advertised for the wild caught fish from some lakes/reservoirs? (Sigrid T.)

Answer: The fish raised and released from DFG hatcheries can be considered “farm raised,” although hatchery rather than farm is a more appropriate term. According to retired DFG Senior Fisheries Biologist Dennis Lee, the fish are fed commercially prepared diets, typically a pellet-type fish feed. Fish meal is the principal ingredient although fish feed usually contains some supplements such as vitamins or shrimp meal, but no hormones. Feeds are analyzed for content and may not contain adulterants such as pesticides.

All DFG hatcheries are routinely monitored by a staff of fish pathologists. If fish become sick, a therapeutic treatment may be prescribed using therapeutic drugs or chemicals approved by FDA for use on food fish. These are either applied to hatchery water or in the case of antibiotics, milled into feed by the manufacturer.

As far as your concerns about mercury warnings, according to Dr. William Cox, DFG Fish Production and Distribution Program Manager, mercury is acquired by fish in waters having high levels of mercury. Fish accumulate mercury by eating small invertebrates, crustaceans and baitfish from those local waters. Larger fish that have lived exclusively in those waters may have elevated levels of mercury. Fish raised in hatcheries are fed diets free of mercury or other contaminants and therefore are free of those chemicals at the time of planting. Health advisory warnings for affected waters are listed in our sport fish regulation booklets, according to California Department of Health Services.